Known rack-and-pinion gears mechanisms 100 (FIG. 2) have a pinion shaft 102 rotatably mounted in a housing 101. The pinion shaft 102 is mounted so as to be rotatable about an axis 103. It is seated in a pinion-shaft hole 104 in the housing 101 and is mounted in the housing 101 in the region of its free end 105 by means of a first rolling-contact bearing 106, which is designed as a locating bearing.
At the other end, the pinion shaft is connected to a steering column (not shown) of a motor vehicle, for example. In the region of the other end, the pinion shaft 102 is mounted in the housing 101 by means of a second rolling-contact bearing 107, which is designed as a non-locating bearing. Between the first rolling-contact bearing 106 and the second rolling-contact bearing 107, the pinion shaft 102 has teeth 108, which mesh with corresponding teeth 109 on a rack 110. The rack 110 is mounted so as to be axially displaceable along its longitudinal axis in the housing 101. Owing to the meshing engagement of the rack 110 with the pinion shaft 102, the imposition of a torque on the pinion shaft 102 gives rise to reaction forces, which act radially relative to the axis 103 and act as bending forces on the rack 110. To compensate for these bending forces, which have a disadvantageous effect on the engagement between the teeth 108 and the corresponding teeth 109, the prior art proposes to impose a counterforce on the rack 110 in the region of the engagement zone, on the rear side 111 of the rack 110, that is, the opposite side from the teeth 109.
The required counter force is generally applied by means of a thrust piece 112. The thrust piece 112 is mounted in a cylindrical opening 113 in the housing 101 in such a way as to be displaceable in a direction perpendicular to the axis 103. The opening 113 is surrounded by a cylindrical wall 114, which is formed integrally on the housing 101. The opening 113 furthermore has a center axis 115, which intersects the longitudinal axis of the rack 110 and the axis 103.
The thrust piece 112 has an essentially cylindrical three-dimensional shape with a first end 116 facing the rack 110 and a second end 117 facing away from the rack 110. The first end 116 has a recess 118, which has an approximately semi-cylindrical cross-section and corresponds to the rear surface 111 of the rack 110. Formed in the thrust piece 112, at the base of the recess 118, is a groove 119, which corresponds to a corresponding web 120 on the rear surface 111 of the rack 110.
Arranged in the center at the second end 117 of the thrust piece 112 is a blind recess 121, with the result that the second end 117 has an end face 122 in the form of a circular ring. Seated in the recess 121 is a spring element, e.g. in the form of a spiral compression spring 123, which is supported by one end on the base of the recess 121. In the region of the end face 122, the opening 113 has an internal thread 124, which extends as far as the axial end of the wall 114. In the region of the axial end, the opening 113 is closed by means of an adjusting/closing nut 125.
On its outer surface, the adjusting/closing nut 125 has an external thread 126, which corresponds to the thread 124, allowing the adjusting/closing nut 125 to be screwed into the opening 113. The adjusting/closing nut 125 furthermore has an annular end face 127, which lies opposite the annular end face 122 of the thrust piece 112 in the assembled condition. In the center, the adjusting/closing nut 125 has a recess 128, which is closed off at the end by a central end wall 129. The compression spring 123 is seated by means of its second end in the recess 128 and is supported on the end wall 129.
A defined clearance S is formed between the annular end face 127 of the adjusting/closing nut 125 and the annular end face 122 of the thrust piece 112. The clearance S is generally 0.15 to 0.30 mm wide and should be set carefully when mounting the thrust piece 112 and the adjusting/closing nut 125.
Examples of known rack-and-pinion gear mechanisms are disclosed in patent documents DE 3151835 C2 and GB 2174474 A each of which describe a rack and pinion gear where the rack-and-pinion gear according to the GB specification is actually designed as a rack-and-pinion steering gear for a motor vehicle. Both rack-and-pinion gears have an adjustable adjusting/closing nut. Through this nut a clearance S is set between the thrust piece and this adjusting/closing nut. The clearance can be seen in both specifications.
With reference again to FIG. 2, the clearance S should be maintained largely unchanged as regards its width during the entire operating time of the rack-and-pinion gear mechanism 100.
To ensure this, it is necessary to secure the adjusting/closing nut 125 against rotation after setting the width of the clearance S, thus preventing any unwanted change in the clearance S during operation.
The adjusting/closing nut 125 is made from steel, for example. To secure the adjusting/closing nut 125 against rotation, the prior art discloses the use of chemical screw-securing means, e.g. screw-securing means that act adhesively and/or in a sealing manner. It is furthermore also customary to caulk the adjusting/closing nut 125 to secure it, one or more blows from a center punch (punch force F) being applied in the region of the front end of the thread 124 and 126. As a result, the wall 114 and the adjusting/closing nut 125 undergo in the region of the thread a local deformation of the material, which thus prevents unintentional loosening and/or rotation of the adjusting/closing nut 125 by form-locking engagement.
Patent document DE 4122528 C2 discloses a method for producing screw-securing means. The screw to be secured is made from two different materials; it has a screw head and a thermoplastics material which is injected on same with positive locking engagement. After assembling the screw the plastics is brought into a fluid state through the supply of heat so that the plastics can flow into the recesses of a housing and after solidification lie contacting the wall of the recess. With this screw-securing means the plastics becomes completely soft or fluid.
As shown in FIG. 2, another known way of securing the adjusting/closing nut 125 against rotation is to deform the wall 114 into an oval shape in plan view in the region of thread engagement by means of radially acting forces to prevent rotation of the adjusting/closing nut 125.
Production methods of this kind to secure the adjusting/closing nut 125 against rotation have the disadvantage that high mechanical forces are introduced into the adjusting nut 125 and the wall 114 and these can have the effect that the preset clearance S changes in an uncontrolled and unintended manner due to the introduction of the mechanical forces, with the result that in some cases the clearance may even be reduced to 0 mm and the thrust piece 112 rests on the adjusting/closing nut 125 in such away that they form a single block. Another disadvantage with the known production methods is that the deformation of the material may give rise to leaks, allowing lubricant to escape from the rack-and-pinion gear and/or damp and/or moisture to penetrate the gear from outside. Moreover, rack-and-pinion gears of this kind are very difficult to service because it is not possible to rule out the housing being destroyed when the adjusting/closing nut 125 is unscrewed.
It is an object of the invention to provide a rack-and-pinion gear which is simple to assemble and is furthermore reliably sealed against lubricant loss and/or damp or moisture penetration. Moreover, the rack-and-pinion gear should be simple and inexpensive to produce and capable of being repaired or adjusted in a simple and non-destructive manner. In addition, the intention is to specify a method for the production of such a rack-and-pinion gear.